Production of Large-Area Bulk Metallic Glass Sheets by Spinning

ABSTRACT

Disclosed herein is a device comprising: vacuum chamber; a stage configured to receive BMG in a molten state or a BMG feedstock, configured to spin, and located in the vacuum chamber; a heater configured to melt the BMG feedstock or to keep BMG in a molten state molten; wherein the stage comprises one or more conduits therein and the conduits are configured to accommodate a cooling fluid. Also disclosed herein is a method of forming a solid BMG sheet, the method comprising: disposing BMG in a molten state onto a stage; spreading the BMG in a molten state into a sheet of BMG in a molten state by spinning the stage; cooling the sheet of BMG in a molten state to form a solid BMG sheet.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.13/803,745, filed Mar. 14, 2013, and entitled “Production of Large-AreaBulk Metallic Glass Sheets,” the entirety of which is incorporated byreference as if fully disclosed herein.

FIELD

The present disclosure is generally related to the production oflarge-area sheets of bulk metallic glass (BMG) alloys.

BACKGROUND

A large portion of the metallic alloys in use today are processed bysolidification casting, at least initially. The metallic alloy is meltedand cast into a metal or ceramic mold, where it solidifies. The mold isstripped away, and the cast metallic piece is ready for use or furtherprocessing. The as-cast structure of most materials produced duringsolidification and cooling depends upon the cooling rate. There is nogeneral rule for the nature of the variation, but for the most part thestructure changes only gradually with changes in cooling rate. On theother hand, for the bulk-solidifying amorphous alloys the change betweenthe amorphous state produced by relatively rapid cooling and thecrystalline state produced by relatively slower cooling is one of kindrather than degree—the two states have distinct properties.

Bulk-solidifying amorphous alloys, or bulk metallic glasses (“BMG”), area recently developed class of metallic materials. These alloys may besolidified and cooled at relatively slow rates, and they retain theamorphous, non-crystalline (i.e., glassy) state at room temperature.This amorphous state can be highly advantageous for certainapplications. If the cooling rate is not sufficiently high, crystals mayform inside the alloy during cooling, so that the benefits of theamorphous state are partially or completely lost. For example, one riskwith the creation of bulk amorphous alloy parts is partialcrystallization due to either slow cooling or impurities in the rawmaterial.

Bulk-solidifying amorphous alloys have been made in a variety ofmetallic systems. They are generally prepared by quenching from abovethe melting temperature to the ambient temperature. Generally, highcooling rates such as one on the order of 10⁵ ° C./sec, are needed toachieve an amorphous structure. The lowest rate by which a bulksolidifying alloy can be cooled to avoid crystallization, therebyachieving and maintaining the amorphous structure during cooling, isreferred to as the “critical cooling rate” for the alloy. In order toachieve a cooling rate higher than the critical cooling rate, heat hasto be extracted from the sample. Thus, the thickness of articles madefrom amorphous alloys often becomes a limiting dimension, which isgenerally referred to as the “critical (casting) thickness.” A criticalthickness of an amorphous alloy can be obtained by heat-flowcalculations, taking into account the critical cooling rate.

Until the early nineties, the processability of amorphous alloys wasquite limited, and amorphous alloys were readily available only inpowder form or in very thin foils or strips with a critical thickness ofless than 100 micrometers. A class of amorphous alloys based mostly onZr and Ti alloy systems was developed in the nineties, and since thenmore amorphous alloy systems based on different elements have beendeveloped. These families of alloys have much lower critical coolingrates of less than 10³ ° C./sec, and thus they have much larger criticalcasting thicknesses than their previous counterparts. However, littlehas been shown regarding how to utilize and/or shape these alloy systemsinto structural components, such as those in consumer electronicdevices. In particular, pre-existing forming or processing methods oftenresult in high product cost when it comes to high aspect ratio products(e.g., thin sheets) or three-dimensional hollow products. Moreover, thepre-existing methods can often suffer the drawbacks of producingproducts that lose many of the desirable mechanical properties asobserved in an amorphous alloy.

SUMMARY

Disclosed herein is a device having a vacuum chamber; a stage configuredto receive BMG in a molten state or a BMG feedstock, configured to spin,and located in the vacuum chamber; a heater configured to melt the BMGfeedstock or to keep BMG in a molten state molten; wherein the stagecomprises one or more conduits therein and the conduits are configuredto accommodate a cooling fluid.

According to an embodiment, the vacuum chamber has a heated region andan unheated region, wherein the heated region is maintained at atemperature at which the BMG feedstock and the BMG in a molten stateremain molten.

According to an embodiment, the device further has a conduit configuredto feed the BMG in a molten state onto the stage.

According to an embodiment, the heated region is heated by induction.

According to an embodiment, the stage is configured to spin at a speedsufficient to spread the BMG in a molten state on the spinning stageinto a BMG sheet.

According to an embodiment, the stage is move from the heated regioninto the unheated region.

According to an embodiment, the BMG feedstock is a bar, rod, or powderof BMG or a composite of materials that form a BMG through melting ofthe BMG feedstock.

According to an embodiment, the cooling fluid is configured to cool andsolidify the BMG sheet at a rate at which the BMG sheet remainsamorphous after solidification.

According to an embodiment, the stage has a heater configured to meltthe BMG feedstock and/or keep the BMG in a molten state molten.

According to an embodiment, the stage has an electrostatic clampconfigured to clamp a substrate onto the stage.

According to an embodiment, the stage has a cavity configured toaccommodate a volume of BMG in a molten state.

Disclosed herein is a method of forming a BMG sheet, having: disposingBMG in a molten state onto a stage; spreading the BMG in a molten stateinto the BMG sheet by spinning the stage; cooling the BMG sheet.

According to an embodiment, disposing BMG in a molten state onto a stagehas disposing a BMG feedstock in a solid form onto the stage and meltingthe BMG feedstock.

According to an embodiment, the stage is in a vacuum chamber.

According to an embodiment, cooling the BMG sheet is performed byflowing a cooling fluid through a conduit in the stage.

According to an embodiment, cooling the BMG sheet is at a rate at whichthe BMG sheet remains amorphous after solidification.

According to an embodiment, the BMG sheet is cooled while the stage isspinning

According to an embodiment, the stage comprises a cavity configured toaccommodate a volume of BMG in a molten state.

According to an embodiment, the BMG sheet has an essentially parabolicsurface.

According to an embodiment the stage is patterned with features so thatan underside (i.e., the side in contact with the stage) of the BMG sheetreplicates the features of the stage. The features may have a size from1-1000 nm, 1 μm 1 mm, or above 1 mm

In one embodiment, a top surface of the BMG is suitable as a reflectivesurface and is essentially free of contamination or texture.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 provides a temperature-viscosity diagram of an exemplary bulksolidifying amorphous alloy.

FIG. 2 provides a schematic of a time-temperature-transformation (TTT)diagram for an exemplary bulk solidifying amorphous alloy.

FIG. 3A shows a device according to an embodiment.

FIG. 3B shows a device according to an embodiment.

FIG. 4 shows the stage that could be used in the device of FIG. 3A or3B, according to an embodiment.

FIG. 5 shows the stage that could be used in the device of FIG. 3A or3B, according to an embodiment.

FIG. 6 shows the stage that could be used in the device of FIG. 3A or3B, according to an embodiment.

FIG. 7 is a flow chart depicting a method of forming a bulk solidifyingamorphous alloy sheet according to an embodiment.

DETAILED DESCRIPTION

All publications, patents, and patent applications cited in thisSpecification are hereby incorporated by reference in their entirety.

The articles “a” and “an” are used herein to refer to one or to morethan one (i.e., to at least one) of the grammatical object of thearticle. By way of example, “a polymer resin” means one polymer resin ormore than one polymer resin. Any ranges cited herein are inclusive. Theterms “substantially” and “about” used throughout this Specification areused to describe and account for small fluctuations. For example, theycan refer to less than or equal to ±5%, such as less than or equal to±2%, such as less than or equal to ±1%, such as less than or equal to±0.5%, such as less than or equal to ±0.2%, such as less than or equalto ±0.1%, such as less than or equal to ±0.05%.

Bulk-solidifying amorphous alloys, or bulk metallic glasses (“BMG”), area recently developed class of metallic materials. These alloys may besolidified and cooled at relatively slow rates, and they retain theamorphous, non-crystalline (i.e., glassy) state at room temperature.Amorphous alloys have many superior properties than their crystallinecounterparts. However, if the cooling rate is not sufficiently high,crystals may form inside the alloy during cooling, so that the benefitsof the amorphous state can be lost. For example, one challenge with thefabrication of bulk amorphous alloy parts is partial crystallization ofthe parts due to either slow cooling or impurities in the raw alloymaterial. As a high degree of amorphicity (and, conversely, a low degreeof crystallinity) is desirable in BMG parts, there is a need to developmethods for casting BMG parts having controlled amount of amorphicity.

FIG. 1 (obtained from U.S. Pat. No. 7,575,040) shows aviscosity-temperature graph of an exemplary bulk solidifying amorphousalloy, from the VIT-001 series of Zr—Ti—Ni—Cu—Be family manufactured byLiquidmetal Technology. It should be noted that there is no clearliquid/solid transformation for a bulk solidifying amorphous metalduring the formation of an amorphous solid. The molten alloy becomesmore and more viscous with increasing undercooling until it approachessolid form around the glass transition temperature. Accordingly, thetemperature of solidification front for bulk solidifying amorphousalloys can be around glass transition temperature, where the alloy willpractically act as a solid for the purposes of pulling out the quenchedamorphous sheet product.

FIG. 2 (obtained from U.S. Pat. No. 7,575,040) shows thetime-temperature-transformation (TTT) cooling curve of an exemplary bulksolidifying amorphous alloy, or TTT diagram. Bulk-solidifying amorphousmetals do not experience a liquid/solid crystallization transformationupon cooling, as with conventional metals. Instead, the highly fluid,non crystalline form of the metal found at high temperatures (near a“melting temperature” Tm) becomes more viscous as the temperature isreduced (near to the glass transition temperature Tg), eventually takingon the outward physical properties of a conventional solid.

Even though there is no liquid/crystallization transformation for a bulksolidifying amorphous metal, a “melting temperature” Tm may be definedas the thermodynamic liquidus temperature of the correspondingcrystalline phase. Under this regime, the viscosity of bulk-solidifyingamorphous alloys at the melting temperature could lie in the range ofabout 0.1 poise to about 10,000 poise, and even sometimes under 0.01poise. A lower viscosity at the “melting temperature” would providefaster and complete filling of intricate portions of the shell/mold witha bulk solidifying amorphous metal for forming the BMG parts.Furthermore, the cooling rate of the molten metal to form a BMG part hasto such that the time-temperature profile during cooling does nottraverse through the nose-shaped region bounding the crystallized regionin the TTT diagram of FIG. 2. In FIG. 2, Tnose is the criticalcrystallization temperature Tx where crystallization is most rapid andoccurs in the shortest time scale.

The supercooled liquid region, the temperature region between Tg and Txis a manifestation of the extraordinary stability againstcrystallization of bulk solidification alloys. In this temperatureregion the bulk solidifying alloy can exist as a high viscous liquid.The viscosity of the bulk solidifying alloy in the supercooled liquidregion can vary between 10¹² Pa s at the glass transition temperaturedown to 10⁵ Pa s at the crystallization temperature, the hightemperature limit of the supercooled liquid region. Liquids with suchviscosities can undergo substantial plastic strain under an appliedpressure. The embodiments herein make use of the large plasticformability in the supercooled liquid region as a forming and separatingmethod.

One needs to clarify something about Tx. Technically, the nose-shapedcurve shown in the TTT diagram describes Tx as a function of temperatureand time. Thus, regardless of the trajectory that one takes whileheating or cooling a metal alloy, when one hits the TTT curve, one hasreached Tx. In FIG. 1( b), Tx is shown as a dashed line as Tx can varyfrom close to Tm to close to Tg.

The schematic TTT diagram of FIG. 2 shows processing methods of diecasting from at or above Tm to below Tg without the time-temperaturetrajectory (shown as (1) as an example trajectory) hitting the TTTcurve. During die casting, the forming takes place substeantiallysimultaneously with fast cooling to avoid the trajectory hitting the TTTcurve. The procssing methods for superplastic forming (SPF) from at orbelow Tg to below Tm without the time-temperature trajectory (shown as(2), (3) and (4) as example trajectories) hitting the TTT curve. In SPF,the amorphous BMG is reheated into the supercooled liquid region wherethe available processing window could be much larger than die casting,resulting in better controllability of the process. The SPF process doesnot require fast cooling to avoid crystallization during cooling. Also,as shown by example trajectories (2), (3) and (4), the SPF can becarried out with the highest temperature during SPF being above Tnose orbelow Tnose, up to about Tm. If one heats up a piece of amorphous alloybut manages to avoid hitting the TTT curve, you have heated “between Tgand Tm”, but one would have not reached Tx.

Typical differential scanning calorimeter (DSC) heating curves ofbulk-solidifying amorphous alloys taken at a heating rate of 20 C/mindescribe, for the most part, a particular trajectory across the TTT datawhere one would likely see a Tg at a certain temperature, a Tx when theDSC heating ramp crosses the TTT crystallization onset, and eventuallymelting peaks when the same trajectory crosses the temperature range formelting. If one heats a bulk-solidifying amorphous alloy at a rapidheating rate as shown by the ramp up portion of trajectories (2), (3)and (4) in FIG. 2, then one could avoid the TTT curve entirely, and theDSC data would show a glass transition but no Tx upon heating. Anotherway to think about it is trajectories (2), (3) and (4) can fall anywherein temperature between the nose of the TTT curve (and even above it) andthe Tg line, as long as it does not hit the crystallization curve. Thatjust means that the horizontal plateau in trajectories might get muchshorter as one increases the processing temperature.

Phase

The term “phase” herein can refer to one that can be found in athermodynamic phase diagram. A phase is a region of space (e.g., athermodynamic system) throughout which all physical properties of amaterial are essentially uniform. Examples of physical propertiesinclude density, index of refraction, chemical composition and latticeperiodicity. A simple description of a phase is a region of materialthat is chemically uniform, physically distinct, and/or mechanicallyseparable. For example, in a system consisting of ice and water in aglass jar, the ice cubes are one phase, the water is a second phase, andthe humid air over the water is a third phase. The glass of the jar isanother separate phase. A phase can refer to a solid solution, which canbe a binary, tertiary, quaternary, or more, solution, or a compound,such as an intermetallic compound. As another example, an amorphousphase is distinct from a crystalline phase.

Metal, Transition Metal, and Non-Metal

The term “metal” refers to an electropositive chemical element. The term“element” in this Specification refers generally to an element that canbe found in a Periodic Table. Physically, a metal atom in the groundstate contains a partially filled band with an empty state close to anoccupied state. The term “transition metal” is any of the metallicelements within Groups 3 to 12 in the Periodic Table that have anincomplete inner electron shell and that serve as transitional linksbetween the most and the least electropositive in a series of elements.Transition metals are characterized by multiple valences, coloredcompounds, and the ability to form stable complex ions. The term“nonmetal” refers to a chemical element that does not have the capacityto lose electrons and form a positive ion.

Depending on the application, any suitable nonmetal elements, or theircombinations, can be used. The alloy (or “alloy composition”) cancomprise multiple nonmetal elements, such as at least two, at leastthree, at least four, or more, nonmetal elements. A nonmetal element canbe any element that is found in Groups 13-17 in the Periodic Table. Forexample, a nonmetal element can be any one of F, Cl, Br, I, At, O, S,Se, Te, Po, N, P, As, Sb, Bi, C, Si, Ge, Sn, Pb, and B. Occasionally, anonmetal element can also refer to certain metalloids (e.g., B, Si, Ge,As, Sb, Te, and Po) in Groups 13-17. In one embodiment, the nonmetalelements can include B, Si, C, P, or combinations thereof. Accordingly,for example, the alloy can comprise a boride, a carbide, or both.

A transition metal element can be any of scandium, titanium, vanadium,chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium,zirconium, niobium, molybdenum, technetium, ruthenium, rhodium,palladium, silver, cadmium, hafnium, tantalum, tungsten, rhenium,osmium, iridium, platinum, gold, mercury, rutherfordium, dubnium,seaborgium, bohrium, hassium, meitnerium, ununnilium, unununium, andununbium. In one embodiment, a BMG containing a transition metal elementcan have at least one of Sc, Y, La, Ac, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd,and Hg. Depending on the application, any suitable transitional metalelements, or their combinations, can be used. The alloy composition cancomprise multiple transitional metal elements, such as at least two, atleast three, at least four, or more, transitional metal elements.

The presently described alloy or alloy “sample” or “specimen” alloy canhave any shape or size. For example, the alloy can have a shape of aparticulate, which can have a shape such as spherical, ellipsoid,wire-like, rod-like, sheet-like, flake-like, or an irregular shape. Theparticulate can have any size. For example, it can have an averagediameter of between about 1 micron and about 100 microns, such asbetween about 5 microns and about 80 microns, such as between about 10microns and about 60 microns, such as between about 15 microns and about50 microns, such as between about 15 microns and about 45 microns, suchas between about 20 microns and about 40 microns, such as between about25 microns and about 35 microns. For example, in one embodiment, theaverage diameter of the particulate is between about 25 microns andabout 44 microns. In some embodiments, smaller particulates, such asthose in the nanometer range, or larger particulates, such as thosebigger than 100 microns, can be used.

The alloy sample or specimen can also be of a much larger dimension. Forexample, it can be a bulk structural component, such as an ingot,housing/casing of an electronic device or even a portion of a structuralcomponent that has dimensions in the millimeter, centimeter, or meterrange.

Solid Solution

The term “solid solution” refers to a solid form of a solution. The term“solution” refers to a mixture of two or more substances, which may besolids, liquids, gases, or a combination of these. The mixture can behomogeneous or heterogeneous. The term “mixture” is a composition of twoor more substances that are combined with each other and are generallycapable of being separated. Generally, the two or more substances arenot chemically combined with each other.

Alloy

In some embodiments, the alloy composition described herein can be fullyalloyed. In one embodiment, an “alloy” refers to a homogeneous mixtureor solid solution of two or more metals, the atoms of one replacing oroccupying interstitial positions between the atoms of the other; forexample, brass is an alloy of zinc and copper. An alloy, in contrast toa composite, can refer to a partial or complete solid solution of one ormore elements in a metal matrix, such as one or more compounds in ametallic matrix. The term alloy herein can refer to both a completesolid solution alloy that can give single solid phase microstructure anda partial solution that can give two or more phases. An alloycomposition described herein can refer to one comprising an alloy or onecomprising an alloy-containing composite.

Thus, a fully alloyed alloy can have a homogenous distribution of theconstituents, be it a solid solution phase, a compound phase, or both.The term “fully alloyed” used herein can account for minor variationswithin the error tolerance. For example, it can refer to at least 90%alloyed, such as at least 95% alloyed, such as at least 99% alloyed,such as at least 99.5% alloyed, such as at least 99.9% alloyed. Thepercentage herein can refer to either volume percent or weightpercentage, depending on the context. These percentages can be balancedby impurities, which can be in terms of composition or phases that arenot a part of the alloy.

Amorphous or Non-Crystalline Solid

An “amorphous” or “non-crystalline solid” is a solid that lacks latticeperiodicity, which is characteristic of a crystal. As used herein, an“amorphous solid” includes “glass” which is an amorphous solid thatsoftens and transforms into a liquid-like state upon heating through theglass transition. Generally, amorphous materials lack the long-rangeorder characteristic of a crystal, though they can possess someshort-range order at the atomic length scale due to the nature ofchemical bonding. The distinction between amorphous solids andcrystalline solids can be made based on lattice periodicity asdetermined by structural characterization techniques such as x-raydiffraction and transmission electron microscopy.

The terms “order” and “disorder” designate the presence or absence ofsome symmetry or correlation in a many-particle system. The terms“long-range order” and “short-range order” distinguish order inmaterials based on length scales.

The strictest form of order in a solid is lattice periodicity: a certainpattern (the arrangement of atoms in a unit cell) is repeated again andagain to form a translationally invariant tiling of space. This is thedefining property of a crystal. Possible symmetries have been classifiedin 14 Bravais lattices and 230 space groups.

Lattice periodicity implies long-range order. If only one unit cell isknown, then by virtue of the translational symmetry it is possible toaccurately predict all atomic positions at arbitrary distances. Theconverse is generally true, except, for example, in quasi-crystals thathave perfectly deterministic tilings but do not possess latticeperiodicity.

Long-range order characterizes physical systems in which remote portionsof the same sample exhibit correlated behavior. This can be expressed asa correlation function, namely the spin-spin correlation function:

G(x,x′)=

s(x), s(x′)

In the above function, s is the spin quantum number and x is thedistance function within the particular system. This function is equalto unity when x=x′ and decreases as the distance |x−x′| increases.Typically, it decays exponentially to zero at large distances, and thesystem is considered to be disordered. If, however, the correlationfunction decays to a constant value at large |x−x′|, then the system canbe said to possess long-range order. If it decays to zero as a power ofthe distance, then it can be called quasi-long-range order. Note thatwhat constitutes a large value of |x−x′| is relative.

A system can be said to present quenched disorder when some parametersdefining its behavior are random variables that do not evolve with time(i.e., they are quenched or frozen)—e.g., spin glasses. It is oppositeto annealed disorder, where the random variables are allowed to evolvethemselves. Embodiments herein include systems comprising quencheddisorder.

The alloy described herein can be crystalline, partially crystalline,amorphous, or substantially amorphous. For example, the alloysample/specimen can include at least some crystallinity, withgrains/crystals having sizes in the nanometer and/or micrometer ranges.Alternatively, the alloy can be substantially amorphous, such as fullyamorphous. In one embodiment, the alloy composition is at leastsubstantially not amorphous, such as being substantially crystalline,such as being entirely crystalline.

In one embodiment, the presence of a crystal or a plurality of crystalsin an otherwise amorphous alloy can be construed as a “crystallinephase” therein. The degree of crystallinity (or “crystallinity” forshort in some embodiments) of an alloy can refer to the amount of thecrystalline phase present in the alloy. The degree can refer to, forexample, a fraction of crystals present in the alloy. The fraction canrefer to volume fraction or weight fraction, depending on the context. Ameasure of how “amorphous” an amorphous alloy is can be amorphicity.Amorphicity can be measured in terms of a degree of crystallinity. Forexample, in one embodiment, an alloy having a low degree ofcrystallinity can be said to have a high degree of amorphicity. In oneembodiment, for example, an alloy having 60 vol % crystalline phase canhave a 40 vol % amorphous phase.

Amorphous Alloy or Amorphous Metal

An “amorphous alloy” is an alloy having an amorphous content of morethan 50% by volume, preferably more than 90% by volume of amorphouscontent, more preferably more than 95% by volume of amorphous content,and most preferably more than 99% to almost 100% by volume of amorphouscontent. Note that, as described above, an alloy high in amorphicity isequivalently low in degree of crystallinity. An “amorphous metal” is anamorphous metal material with a disordered atomic-scale structure. Incontrast to most metals, which are crystalline and therefore have ahighly ordered arrangement of atoms, amorphous alloys arenon-crystalline. Materials in which such a disordered structure isproduced directly from the liquid state during cooling are sometimesreferred to as “glasses.”Accordingly, amorphous metals are commonlyreferred to as “metallic glasses” or “glassy metals.” In one embodiment,a bulk metallic glass (“BMG”) can refer to an alloy, of which themicrostructure is at least partially amorphous. However, there areseveral ways besides extremely rapid cooling to produce amorphousmetals, including physical vapor deposition, solid-state reaction, ionirradiation, melt spinning, and mechanical alloying. Amorphous alloyscan be a single class of materials, regardless of how they are prepared.

Amorphous metals can be produced through a variety of quick-coolingmethods. For instance, amorphous metals can be produced by sputteringmolten metal onto a spinning metal disk. The rapid cooling, on the orderof millions of degrees a second, can be too fast for crystals to form,and the material is thus “locked in” a glassy state. Also, amorphousmetals/alloys can be produced with critical cooling rates low enough toallow formation of amorphous structures in thick layers—e.g., bulkmetallic glasses.

The terms “bulk metallic glass” (“BMG”), bulk amorphous alloy (“BAA”),and bulk solidifying amorphous alloy are used interchangeably herein.They refer to amorphous alloys having the smallest dimension at least inthe millimeter range. For example, the dimension can be at least about0.5 mm, such as at least about 1 mm, such as at least about 2 mm, suchas at least about 4 mm, such as at least about 5 mm, such as at leastabout 6 mm, such as at least about 8 mm, such as at least about 10 mm,such as at least about 12 mm Depending on the geometry, the dimensioncan refer to the diameter, radius, thickness, width, length, etc. A BMGcan also be a metallic glass having at least one dimension in thecentimeter range, such as at least about 1.0 cm, such as at least about2.0 cm, such as at least about 5.0 cm, such as at least about 10.0 cm.In some embodiments, a BMG can have at least one dimension at least inthe meter range. A BMG can take any of the shapes or forms describedabove, as related to a metallic glass. Accordingly, a BMG describedherein in some embodiments can be different from a thin film made by aconventional deposition technique in one important aspect—the former canbe of a much larger dimension than the latter.

Amorphous metals can be an alloy rather than a pure metal. The alloysmay contain atoms of significantly different sizes, leading to low freevolume (and therefore having viscosity up to orders of magnitude higherthan other metals and alloys) in a molten state. The viscosity preventsthe atoms from moving enough to form an ordered lattice. The materialstructure may result in low shrinkage during cooling and resistance toplastic deformation. The absence of grain boundaries, the weak spots ofcrystalline materials in some cases, may, for example, lead to betterresistance to wear and corrosion. In one embodiment, amorphous metals,while technically glasses, may also be much tougher and less brittlethan oxide glasses and ceramics.

Thermal conductivity of amorphous materials may be lower than that oftheir crystalline counterparts. To achieve formation of an amorphousstructure even during slower cooling, the alloy may be made of three ormore components, leading to complex crystal units with higher potentialenergy and lower probability of formation. The formation of amorphousalloy can depend on several factors: the composition of the componentsof the alloy; the atomic radius of the components (preferably with asignificant difference of over 12% to achieve high packing density andlow free volume); and the negative heat of mixing the combination ofcomponents, inhibiting crystal nucleation and prolonging the time themolten metal stays in a supercooled state. However, as the formation ofan amorphous alloy is based on many different variables, it can bedifficult to make a prior determination of whether an alloy compositionwould form an amorphous alloy.

Amorphous alloys, for example, of boron, silicon, phosphorus, and otherglass formers with magnetic metals (iron, cobalt, nickel) may bemagnetic, with low coercivity and high electrical resistance. The highresistance leads to low losses by eddy currents when subjected toalternating magnetic fields, a property useful, for example, astransformer magnetic cores.

Amorphous alloys may have a variety of potentially useful properties. Inparticular, they tend to be stronger than crystalline alloys of similarchemical composition, and they can sustain larger reversible (“elastic”)deformations than crystalline alloys. Amorphous metals derive theirstrength directly from their non-crystalline structure, which can havenone of the defects (such as dislocations) that limit the strength ofcrystalline alloys. For example, one modem amorphous metal, known asVitreloy™, has a tensile strength that is almost twice that ofhigh-grade titanium. In some embodiments, metallic glasses at roomtemperature are not ductile and tend to fail suddenly when loaded intension, which limits the material applicability in reliability-criticalapplications, as the impending failure is not evident. Therefore, toovercome this challenge, metal matrix composite materials having ametallic glass matrix containing dendritic particles or fibers of aductile crystalline metal can be used. Alternatively, a BMG low inelement(s) that tend to cause embitterment (e.g., Ni) can be used. Forexample, a Ni-free BMG can be used to improve the ductility of the BMG.

Another useful property of bulk amorphous alloys is that they can betrue glasses; in other words, they can soften and flow upon heating.This can allow for easy processing, such as by injection molding, inmuch the same way as polymers. As a result, amorphous alloys can be usedfor making sports equipment, medical devices, electronic components andequipment, and thin films. Thin films of amorphous metals can bedeposited as protective coatings via a high velocity oxygen fueltechnique.

A material can have an amorphous phase, a crystalline phase, or both.The amorphous and crystalline phases can have the same chemicalcomposition and differ only in the microstructure—i.e., one amorphousand the other crystalline. Microstructure in one embodiment refers tothe structure of a material as revealed by a microscope at 25×magnification or higher. Alternatively, the two phases can havedifferent chemical compositions and microstructures. For example, acomposition can be partially amorphous, substantially amorphous, orcompletely amorphous.

As described above, the degree of amorphicity (and conversely the degreeof crystallinity) can be measured by fraction of crystals present in thealloy. The degree can refer to volume fraction of weight fraction of thecrystalline phase present in the alloy. A partially amorphouscomposition can refer to a composition of at least about 5 vol % ofwhich is of an amorphous phase, such as at least about 10 vol %, such asat least about 20 vol %, such as at least about 40 vol %, such as atleast about 60 vol %, such as at least about 80 vol %, such as at leastabout 90 vol %. The terms “substantially” and “about” have been definedelsewhere in this application. Accordingly, a composition that is atleast substantially amorphous can refer to one of which at least about90 vol % is amorphous, such as at least about 95 vol %, such as at leastabout 98 vol %, such as at least about 99 vol %, such as at least about99.5 vol %, such as at least about 99.8 vol %, such as at least about99.9 vol %. In one embodiment, a substantially amorphous composition canhave some incidental, insignificant amount of crystalline phase presenttherein.

In one embodiment, an amorphous alloy composition can be homogeneouswith respect to the amorphous phase. A substance that is uniform incomposition is homogeneous. This is in contrast to a substance that isheterogeneous. The term “composition” refers to the chemical compositionand/or microstructure in the substance. A substance is homogeneous whena volume of the substance is divided in half and both halves havesubstantially the same composition. For example, a particulatesuspension is homogeneous when a volume of the particulate suspension isdivided in half and both halves have substantially the same volume ofparticles. However, it might be possible to see the individual particlesunder a microscope. Another example of a homogeneous substance is airwhere different ingredients therein are equally suspended, though theparticles, gases and liquids in air can be analyzed separately orseparated from air.

A composition that is homogeneous with respect to an amorphous alloy canrefer to one having an amorphous phase substantially uniformlydistributed throughout its microstructure. In other words, thecomposition macroscopically comprises a substantially uniformlydistributed amorphous alloy throughout the composition. In analternative embodiment, the composition can be of a composite, having anamorphous phase having therein a non-amorphous phase. The non-amorphousphase can be a crystal or a plurality of crystals. The crystals can bein the form of particulates of any shape, such as spherical, ellipsoid,wire-like, rod-like, sheet-like, flake-like, or an irregular shape. Inone embodiment, it can have a dendritic form. For example, an at leastpartially amorphous composite composition can have a crystalline phasein the shape of dendrites dispersed in an amorphous phase matrix; thedispersion can be uniform or non-uniform, and the amorphous phase andthe crystalline phase can have the same or a different chemicalcomposition. In one embodiment, they have substantially the samechemical composition. In another embodiment, the crystalline phase canbe more ductile than the BMG phase.

The methods described herein can be applicable to any type of amorphousalloy. Similarly, the amorphous alloy described herein as a constituentof a composition or article can be of any type. The amorphous alloy cancomprise the element Zr, Hf, Ti, Cu, Ni, Pt, Pd, Fe, Mg, Au, La, Ag, Al,Mo, Nb, Be, or combinations thereof. Namely, the alloy can include anycombination of these elements in its chemical formula or chemicalcomposition. The elements can be present at different weight or volumepercentages. For example, an iron “based” alloy can refer to an alloyhaving a non-insignificant weight percentage of iron present therein,the weight percent can be, for example, at least about 20 wt %, such asat least about 40 wt %, such as at least about 50 wt %, such as at leastabout 60 wt %, such as at least about 80 wt %. Alternatively, in oneembodiment, the above-described percentages can be volume percentages,instead of weight percentages. Accordingly, an amorphous alloy can bezirconium-based, titanium-based, platinum-based, palladium-based,gold-based, silver-based, copper-based, iron-based, nickel-based,aluminum-based, molybdenum-based, and the like. The alloy can also befree of any of the aforementioned elements to suit a particular purpose.For example, in some embodiments, the alloy, or the compositionincluding the alloy, can be substantially free of nickel, aluminum,titanium, beryllium, or combinations thereof. In one embodiment, thealloy or the composite is completely free of nickel, aluminum, titanium,beryllium, or combinations thereof.

For example, the amorphous alloy can have the formula (Zr, Ti)_(a)(Ni,Cu, Fe)_(b)(Be, Al, Si, B)_(c), wherein a, b, and c each represents aweight or atomic percentage. In one embodiment, a is in the range offrom 30 to 75, b is in the range of from 5 to 60, and c is in the rangeof from 0 to 50 in atomic percentages. Alternatively, the amorphousalloy can have the formula (Zr, Ti)_(a)(Ni, Cu)_(b)(Be)_(c), wherein a,b, and c each represents a weight or atomic percentage. In oneembodiment, a is in the range of from 40 to 75, b is in the range offrom 5 to 50, and c is in the range of from 5 to 50 in atomicpercentages. The alloy can also have the formula (Zr, Ti)_(a)(Ni,Cu)_(b)(Be)_(c), wherein a, b, and c each represents a weight or atomicpercentage. In one embodiment, a is in the range of from 45 to 65, b isin the range of from 7.5 to 35, and c is in the range of from 10 to 37.5in atomic percentages. Alternatively, the alloy can have the formula(Zr)_(a)(Nb, Ti)_(b)(Ni, Cu)_(c)(Al)_(d), wherein a, b, c, and d eachrepresents a weight or atomic percentage. In one embodiment, a is in therange of from 45 to 65, b is in the range of from 0 to 10, c is in therange of from 20 to 40 and d is in the range of from 7.5 to 15 in atomicpercentages. One exemplary embodiment of the aforedescribed alloy systemis a Zr—Ti—Ni—Cu—Be based amorphous alloy under the trade name Vitreloy™such as Vitreloy-1 and Vitreloy-101, as fabricated by LiquidmetalTechnologies, CA, USA. Some examples of amorphous alloys of thedifferent systems are provided in Table 1.

The amorphous alloys can also be ferrous alloys, such as (Fe, Ni, Co)based alloys. Examples of such compositions are disclosed in U.S. Pat.Nos. 6,325,868; 5,288,344; 5,368,659; 5,618,359; and 5,735,975, Inoue etal., Appl. Phys. Lett., Volume 71, p 464 (1997), Shen et al., Mater.Trans., JIM, Volume 42, p 2136 (2001), and Japanese Patent ApplicationNo. 200126277 (Pub. No. 2001303218 A). One exemplary composition isFe₇₂Al₅Ga₂P₁₁C₆B₄. Another example is Fe₇₂Al₇Zr₁₀Mo₅W₂B₁₅. Anotheriron-based alloy system that can be used in the coating herein isdisclosed in U.S. Patent Application Publication No. 2010/0084052,wherein the amorphous metal contains, for example, manganese (1 to 3atomic %), yttrium (0.1 to 10 atomic %), and silicon (0.3 to 3.1 atomic%) in the range of composition given in parentheses; and that containsthe following elements in the specified range of composition given inparentheses: chromium (15 to 20 atomic %), molybdenum (2 to 15 atomic%), tungsten (1 to 3 atomic %), boron (5 to 16 atomic %), carbon (3 to16 atomic %), and the balance iron.

The aforedescribed amorphous alloy systems can further includeadditional elements, such as additional transition metal elements,including Nb, Cr, V, and Co. The additional elements can be present atless than or equal to about 30 wt %, such as less than or equal to about20 wt %, such as less than or equal to about 10 wt %, such as less thanor equal to about 5 wt %. In one embodiment, the additional, optionalelement is at least one of cobalt, manganese, zirconium, tantalum,niobium, tungsten, yttrium, titanium, vanadium and hafnium to formcarbides and further improve wear and corrosion resistance. Furtheroptional elements may include phosphorous, germanium and arsenic,totaling up to about 2%, and preferably less than 1%, to reduce meltingpoint. Otherwise incidental impurities should be less than about 2% andpreferably 0.5%.

TABLE 1 Exemplary amorphous alloy compositions Alloy Atm % Atm % Atm %Atm % Atm % Atm % 1 Zr Ti Cu Ni Be 41.20% 13.80% 12.50% 10.00% 22.50% 2Zr Ti Cu Ni Be 44.00% 11.00% 10.00% 10.00% 25.00% 3 Zr Ti Cu Ni Nb Be56.25% 11.25%  6.88%  5.63%  7.50% 12.50% 4 Zr Ti Cu Ni Al Be 64.75% 5.60% 14.90% 11.15%  2.60% 1.00% 5 Zr Ti Cu Ni Al 52.50%  5.00% 17.90%14.60% 10.00% 6 Zr Nb Cu Ni Al 57.00%  5.00% 15.40% 12.60% 10.00% 7 ZrCu Ni Al Sn 50.75% 36.23%  4.03%  9.00% 0.50% 8 Zr Ti Cu Ni Be 46.75% 8.25%  7.50% 10.00% 27.50% 9 Zr Ti Ni Be 21.67% 43.33%  7.50% 27.50% 10Zr Ti Cu Be 35.00% 30.00%  7.50% 27.50% 11 Zr Ti Co Be 35.00% 30.00% 6.00% 29.00% 12 Au Ag Pd Cu Si 49.00%  5.50%  2.30% 26.90% 16.30% 13 AuAg Pd Cu Si 50.90%  3.00%  2.30% 27.80% 16.00% 14 Pt Cu Ni P 57.50%14.70%  5.30% 22.50% 15 Zr Ti Nb Cu Be 36.60% 31.40%  7.00%  5.90%19.10% 16 Zr Ti Nb Cu Be 38.30% 32.90%  7.30%  6.20% 15.30% 17 Zr Ti NbCu Be 39.60% 33.90%  7.60%  6.40% 12.50% 18 Cu Ti Zr Ni 47.00% 34.00%11.00%  8.00% 19 Zr Co Al 55.00% 25.00% 20.00%

In some embodiments, a composition having an amorphous alloy can includea small amount of impurities. The impurity elements can be intentionallyadded to modify the properties of the composition, such as improving themechanical properties (e.g., hardness, strength, fracture mechanism,etc.) and/or improving the corrosion resistance. Alternatively, theimpurities can be present as inevitable, incidental impurities, such asthose obtained as a byproduct of processing and manufacturing. Theimpurities can be less than or equal to about 10 wt %, such as about 5wt %, such as about 2 wt %, such as about 1 wt %, such as about 0.5 wt%, such as about 0.1 wt %. In some embodiments, these percentages can bevolume percentages instead of weight percentages. In one embodiment, thealloy sample/composition consists essentially of the amorphous alloy(with only a small incidental amount of impurities). In anotherembodiment, the composition includes the amorphous alloy (with noobservable trace of impurities).

In one embodiment, the final parts exceeded the critical castingthickness of the bulk solidifying amorphous alloys.

In embodiments herein, the existence of a supercooled liquid region inwhich the bulk-solidifying amorphous alloy can exist as a high viscousliquid allows for superplastic forming. Large plastic deformations canbe obtained. The ability to undergo large plastic deformation in thesupercooled liquid region is used for the forming and/or cuttingprocess. As oppose to solids, the liquid bulk solidifying alloy deformslocally which drastically lowers the required energy for cutting andforming The ease of cutting and forming depends on the temperature ofthe alloy, the mold, and the cutting tool. As higher is the temperature,the lower is the viscosity, and consequently easier is the cutting andforming

Embodiments herein can utilize a thermoplastic-forming process withamorphous alloys carried out between Tg and Tx, for example. Herein, Txand Tg are determined from standard DSC measurements at typical heatingrates (e.g. 20° C./min) as the onset of crystallization temperature andthe onset of glass transition temperature.

The amorphous alloy components can have the critical casting thicknessand the final part can have thickness that is thicker than the criticalcasting thickness. Moreover, the time and temperature of the heating andshaping operation is selected such that the elastic strain limit of theamorphous alloy could be substantially preserved to be not less than1.0%, and preferably not being less than 1.5%. In the context of theembodiments herein, temperatures around glass transition means theforming temperatures can be below glass transition, at or around glasstransition, and above glass transition temperature, but preferably attemperatures below the crystallization temperature T_(x). The coolingstep is carried out at rates similar to the heating rates at the heatingstep, and preferably at rates greater than the heating rates at theheating step. The cooling step is also achieved preferably while theforming and shaping loads are still maintained.

Electronic Devices

The embodiments herein can be valuable in the fabrication of electronicdevices using a BMG. An electronic device herein can refer to anyelectronic device known in the art. For example, it can be a telephone,such as a cell phone, and a land-line phone, or any communicationdevice, such as a smart phone, including, for example an iPhone™, and anelectronic email sending/receiving device. It can be a part of adisplay, such as a digital display, a TV monitor, an electronic-bookreader, a portable web-browser (e.g., iPad™), and a computer monitor. Itcan also be an entertainment device, including a portable DVD player,conventional DVD player, Blue-Ray disk player, video game console, musicplayer, such as a portable music player (e.g., iPod™), etc. It can alsobe a part of a device that provides control, such as controlling thestreaming of images, videos, sounds (e.g., Apple TV™), or it can be aremote control for an electronic device. It can be a part of a computeror its accessories, such as the hard drive tower housing or casing,laptop housing, laptop keyboard, laptop track pad, desktop keyboard,mouse, and speaker. The article can also be applied to a device such asa watch or a clock.

A large-area metal sheet is a useful form for manufacture. It could bewelded to form parts such as cases, enclosures or tanks. It could be cut(e.g., water-jet or laser) into parts such as springs, plates, rings,etc. It could also be useful as feedstock for processes such as blowmolding, thermoplastic forming or coining, etc.

Making BMG in to a large-area sheet poses certain unique challenges dueto the properties of BMG. For example, if the process of making BMG intoa large-area sheet involves too much heating (especially when thelarge-area sheet is thin), the sheet may cease to be essentiallyamorphous. Minimizing the thermal history of such a process has toinvolve would increase the amount of time available to a downstreamoperation that uses the sheet to make parts before the sheet loses itsamorphousness.

Spin coating is a process to apply uniform thin films to a substrate. Inthe spin coating process, a liquid is placed on the substrate, which isthen rotated at high speed to spread the liquid by centrifugal force. Amachine used for spin coating is called a spin coater, or simplyspinner. Rotation may be continued while the liquid spins off the edgesof the substrate, until the desired thickness of the film is achieved.The higher the angular speed of spinning, the thinner the film. Thethickness of the film also depends on the viscosity of the liquid andthe duration the spinning Spin coating is widely used inmicrofabrication, where it can be used to create thin films withthicknesses below 10 nm. It is used intensively in photolithography, todeposit layers of photoresist about 1 micrometre thick. Photoresist istypically spun at 20 to 80 revolutions per second for 30 to 60 seconds.

Similar spinning technique as that for making crown glass can be usedfor BMG sheets. In one embodiment, the process of making BMG sheets madeby the spinning process could be called a “crown glass” process. In thisprocess, a BMG sheet can be formed into a “crown” or hollow globe, andthen transferred from the blowpipe to a punty and then flattened byreheating and spinning out the bowl-shaped piece of the BMG (bullion)into a flat disk by centrifugal force, up to 5 or 6 feet (1.5 to 1.8 m)in diameter. The disk can then be cut to the size required.

In an embodiment illustrated in FIG. 3A, a device configured to makingBMG sheets by spinning comprises a vacuum chamber. The vacuum chambermay be divided into a heated region 305 and an unheated region 306. Thedevice comprises a mechanism such as a conduit 301, configured to feedBMG in a molten state onto a spinning stage 320. The conduit 301 maycomprise a ceramic or graphite funnel surrounded by an induction coil.The BMG in a molten state is maintained in the molten state when thespinning stage 320 is in the heated region 305. The heated region 305may be heated by any suitable method sufficient to maintain atemperature at which the BMG is molten. For example, induction coils 310may be used to inductively heat the BMG in a molten state on thespinning stage 320. The spinning stage 320 is configured to spin at aspeed sufficient to spread the BMG in a molten state on the spinningstage 320 into a BMG sheet by centrifugal force. The spinning stage 320may also be configured to move from the heated region 305 into theunheated region 306 to cool the BMG sheet. Alternatively, the spinningstage may remain in the heated region 305 and the heating is turned offto cool the BMG sheet. In an embodiment, the spinning stage 320comprises a high thermal conductivity ceramic, chrome and/orchromium0nitride coated copper. The spinning stage 320 may compriseconduits 330 configured to accommodate cooling fluids. The coolingfluids can cool and solidify the BMG sheet on the spinning stage at arate at which the BMG sheet remains amorphous after solidification. Thespinning stage 320 is preferably able to withstand high temperatures upto about 1000° C.

The thickness of the BMG sheet can be estimated as

$\frac{a}{\omega \sqrt{t}},$

where ω is the angular velocity of the spinning stage 320, t is theduration of the spinning and a is an empirical constant.

In an alternative setup illustrated in FIG. 3B, instead of feeding BMGin a molten state onto the spinning stage 320, a BMG feedstock 401 insolid form is placed on the spinning stage and the BMG feedstock ismelted on the stage before being spun into a BMG sheet. The BMGfeedstock 401 could be a bar, rod, or powder of BMG or a composite ofmaterials that form a BMG through melting of the BMG feedstock 401.

In an embodiment illustrated in FIG. 4, the spinning stage 320 maycomprise conduits 520 configured to accommodate cooling fluids. Thecooling fluids can cool and solidify the BMG sheet on the spinning stageat a rate at which the BMG sheet remains amorphous after solidification.The spinning stage 320 may comprises a heater 510 configured to melt theBMG feedstock 401 and/or keep any BMG on the spinning stage 320 in themolten state during the spinning.

In an embodiment illustrated in FIG. 5, the spinning stage 320 maycomprise an electrostatic clamp 610 configured to clamp a substrate(e.g., silicon, ceramic) onto the spinning stage 320 so that the BMGsheet forms on the substrate.

In an embodiment illustrated in FIG. 6, a spinning stage 400 may have acavity configured to accommodate a volume of BMG in a molten state 801.As the spinning stage 400 spins, the BMG in a molten state 801 forms anessentially parabolic surface 850. The BMG in a molten state 801 can becooled to the solid state while the spinning stage 400 spins. Theparabolic surface 850 is thus retained in the solid state. The parabolicsurface 850 of the BMG may be configured as a minor for use in anoptical system.

A method of forming a BMG sheet is shown in the flow chart of FIG. 7.The method includes: disposing BMG in a molten state onto a stage;spreading the BMG in a molten state into the BMG sheet by spinning thestage; cooling the BMG sheet.

In an embodiment, the BMG is essentially free of iron. In an embodiment,the BMG is essentially free of nickel. In an embodiment, the BMG isessentially free of cobalt. In an embodiment, the BMG is essentiallyfree of gold, silver and platinum. In an embodiment the BMG is notferromagnetic. In an embodiment, the BMG is a composition listed inTable 1.

While the invention is described and illustrated here in the context ofa limited number of embodiments, the invention may be embodied in manyforms without departing from the spirit of the essential characteristicsof the invention. The illustrated and described embodiments, includingwhat is described in the abstract of the disclosure, are therefore to beconsidered in all respects as illustrative and not restrictive. Thescope of the invention is indicated by the appended claims rather thanby the foregoing description, and all changes that come within themeaning and range of equivalency of the claims are intended to beembraced therein.

We claim:
 1. A method of forming a solid BMG sheet, comprising:disposing BMG in a molten state onto a stage; spreading the BMG in amolten state into the BMG sheet by spinning the stage; cooling the BMGin a molten state to form the solid BMG sheet.
 2. The method of claim 1,wherein disposing BMG in a molten state onto a stage comprises disposinga BMG feedstock in a solid form onto the stage and melting the BMGfeedstock.
 3. The method of claim 1, wherein the stage is in a vacuumchamber.
 4. The method of claim 1, wherein cooling the BMG in a moltenstate comprises flowing a cooling fluid through a conduit in the stage.5. The method of claim 1, wherein cooling the BMG in a molten state isat a rate at which the solid BMG sheet remains amorphous aftersolidification.
 6. The method of claim 1, wherein the BMG in a moltenstate is cooled while the stage is spinning.
 7. The method of claim 1,wherein the stage comprises a cavity configured to accommodate a volumeof BMG in a molten state.
 8. The method of claim 1, wherein the BMGsheet comprises an essentially parabolic surface.